In a previous life, he was a demon king, and in this life, a hero who was transferred to this world works hard to search for his comrades from his past life.

A high school student named Nishiya Yomichi, who claims to be ordinary despite possessing memories from his past life, is transported to a world where he and his classmates spent their previous lives as heroes. "No, wait—I was a Demon Lord in my past life, so what am I supposed to do?" While being caught up in unrelated romantic comedies—protecting his sister's chastity from a mentally unstable, yandere-looking beautiful girl with a clean appearance, receiving jealousy and love advice from a righteous handsome guy, and giving his corrupt perfect superhuman sister ideas for her delusions—he pushes forward toward his goal. His only objective is to investigate the whereabouts of his former comrades whom he could call family in his past life. He doesn't become the strongest, nor is he looked down upon or bullied, nor does he live a slow life. It's simply a story of him and his classmates who became heroes, along with the people of this other world, spinning each other around in circles.